Corrosion of 310 stainless steel in H2 H2O-H2S gas mixtures; studies at constant temperature and fixed oxygen potential

Corrosion of SAE 310 stainless steel in H2-H2O-H2S gas mixtures was studied at a constant temperature of 1150 K. Reactive gas mixtures were chosen to yield a constant oxygen potential of approximately 6 × 10-13 Nm-2 and sulfur potentials ranging from 0.19 × 10-2 Nm-2 to 33 × 10-2 Nm-2. The kinetics of corrosion were determined using a thermobalance, and the scales were analyzed using metallography, scanning electron microscopy, and energy dispersive X-ray analysis. Two corrosion regimes, which were dependent on sulfur potential, were identified. At high sulfur potentials (P S 2 ± 2.7 × 10-2 Nm-2) the corrosion rates were high, the kinetics obeyed a linear rate equation, and the scales consisted mainly of sulfide phases similar to those observed from pure sulfidation. At low sulfur potentials (P S 2 ± 0.19 × 10-2 Nm-2) the corrosion rates were low, the kinetics obeyed a parabolic rate equation, and scales consisted mainly of oxide phases. Thermochemical diagrams for the Fe-Cr-S-O, Fe-Ni-S-O, Cr-Ni-S-O, and Si-Cr-S-O systems were constructed, and the experimental results are discussed in relation to these diagrams. Based on this comparison, reasonable corrosion mechanisms were developed. At high sulfur potentials, oxide and sulfide phases initially nucleate as separate islands. Overgrowth of the oxide by the sulfide occurs and an exchange reaction governs the corrosion process. Preoxidation at low oxygen potentials and 1150 K is beneficial in suppressing sulfidation at high sulfur potentials.

Solubility and activity of oxygen in liquid nickel in equilibrium with -Al2O3 and NiO.(1+x)Al2O3

The limiting solubility of oxygen in liquid nickel in equilibrium withα-alumina and nickel aluminate has been measured by inert gas fusion analysis of suction samples in the temperature range 1730 to 1975 K. The corresponding oxygen potential has been monitored by a solid electrolyte cell consisting of calcia stabilized zirconia as the electrolyte and Mo + MoO2 as the reference electrode. The results can be summarized by the following equations: log(at. pct O) = \frac - 10,005T + 4.944 ( ±0.015)log(atpctO)=T−10005+4944(0015) % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn DmO2 /4.606RT = log P O2 1/2 = \frac - 13,550T + 4.411 ( ±0.009)O24606RT=logPO212=T−13550+4411(0009) From simultaneous measurements of the potential and concentration of oxygen in melts, not in thermodynamic equilibrium with alumina and aluminate phases, information on the composition dependence of the activity coefficient and the standard free energy of solution of oxygen is obtained. For the reaction, $\frac{1}{2} O_2 \to \underset{\raise0.3em\hbox{$Missing close brace ΔG o = -72,930 - 7.11T (±840) J gr.at.–1 = + 0.216 at. pct OlogfO=T−500+0216atpctO where the standard state for dissolved oxygen is that which makes the value of activity equal to the concentration (in at. pct) in the limit as concentration approaches zero. The oxygen solubility in liquid nickel in equilibrium with solid NiO, evaluated from thermodynamic data, is compared with information reported in the literature. Implications of the results to the deoxidation equilibria of aluminum in nickel are discussed.

Use of CaC12 as a chlorinating agent for oxides - A thermodynamic analysis

Presented is a thermodynamic feasibility analysis of extracting base metal chlorides fiom low-grade,multimetallic oxide ores using CaClz as a chlorinating agent in the presence of SOz undoz. The oxides react to form corresponding chlorides, while CaClz is converted to CaS04. The Ellingham diagram is usedfor comparing the standard Gibbs' fiee energy chanlpef or the su(fation-chlorinationr eaction of a large number of oxides. Except for alumina, silica and chromia, most of the other metal oxides will be converted to their respective chlorides. The volatile chlorides can be condensed, and the chlorides present in the condensed state can be leached. A process is proposed that uses a nontoxic chlorinating agent and gives an eficient sepurutiort cftlte metallic vuluesfr.om the garlgue.

System Nd-Pd-O: Phase diagram and thermodynamic properties of oxides using a solid-state cell with advanced features

An isothermal section of the phase diagram for the system Nd-Pd-O at 1350 K has been established by equilibration of samples representing 13 different compositions and phase identification after quenching by optical and scanning electron microscopy, x-ray diffraction, and energy dispersive analysis of x-rays. The binary oxides PdO and NdO were not stable at 1350 K. Two ternary oxides Nd4PdO7 and Nd2Pd2O5 were identified. Solid and liquid alloys, as well as the intermetallics NdPd3 and NdPd5, were found to be in equilibrium with Nd2O3. Based on the phase relations, three solidstate cells were designed to measure the Gibbs energies of formation of PdO and the two ternary oxides. An advanced version of the solid-state cell incorporating a buffer electrode was used for high-temperature thermodynamic measurements. The function of the buffer electrode, placed between reference and working electrodes, was to absorb the electrochemical flux of the mobile species through the solid electrolyte caused by trace electronic conductivity. The buffer electrode prevented polarization of the measuring electrode and ensured accurate data. Yttria-stabilized zirconia was used as the solid electrolyte and pure oxygen gas at a pressure of 0.1 MP a as the reference electrode. Electromotive force measurements, conducted from 950 to 1425 K, indicated the presence of a third ternary oxide Nd2PdO4, stable below 1135 (±10) K. Additional cells were designed to study this compound. The standard Gibbs energy of formation of PdO (†f G 0) was measured from 775 to 1125 Kusing two separate cell designs against the primary reference standard for oxygen chemical potential. Based on the thermodynamic information, chemical potential diagrams for the system Nd-Pd-O were also developed.

The standard enthalpy and entropy of formation of Rh2O3 - A third-law optimization

The standard Gibbs energy of formation of Rh203 at high temperature has been determined recently with high precision. The new data are significantly different from those given in thermodynamic compilations.Accurate values for enthalpy and entropy of formation at 298.15 K could not be evaluated from the new data,because reliable values for heat capacity of Rh2O3 were not available. In this article, a new measurement of the high temperature heat capacity of Rh2O3 using differential scanning calorimetry (DSC) is presented.The new values for heat capacity also differ significantly from those given in compilations. The information on heat capacity is coupled with standard Gibbs energy of formation to evaluate values for standard enthalpy and entropy of formation at 289.15 K using a multivariate analysis. The results suggest a major revision in thermodynamic data for Rh2O3. For example, it is recommended that the standard entropy of Rh203 at 298.15 K be changed from 106.27 J mol-' K-'given in the compilations of Barin and Knacke et al. to 75.69 J mol-' K". The recommended revision in the standard enthalpy of formation is from -355.64 kJ mol-'to -405.53 kJ mol".

Variation of the gas and radiation content in the sub-Keplerian accretion disk around black holes and its impact to the solutions

We investigate the variation of the gas and the radiation pressure in accretion disks during the infall of matter to the black hole and its effect to the flow. While the flow far away from the black hole might be non-relativistic, in the vicinity of the black hole it is expected to be relativistic behaving more like radiation. Therefore, the ratio of gas pressure to total pressure (beta) and the underlying polytropic index (gamma) should not be constant throughout the flow. We obtain that accretion flows exhibit significant variation of beta and then gamma, which affects solutions described in the standard literature based on constant beta. Certain solutions for a particular set of initial parameters with a constant beta do not exist when the variation of beta is incorporated appropriately. We model the viscous sub-Keplerian accretion disk with a nonzero component of advection and pressure gradient around black holes by preserving the conservations of mass, momentum, energy, supplemented by the evolution of beta. By solving the set of five coupled differential equations, we obtain the thermo-hydrodynamical properties of the flow. We show that during infall, beta of the flow could vary up to similar to 300%, while gamma up to similar to 20%. This might have a significant impact to the disk solutions in explaining observed data, e.g. super-luminal jets from disks, luminosity, and then extracting fundamental properties from them. Hence any conclusion based on constant gamma and beta should be taken with caution and corrected. (C) 2011 Elsevier B.V. All rights reserved.

Frequency response analysis of layered ground in Ahmedabad during Bhuj earthquake

This paper presents the results of seismic response analysis of layered ground in Ahmedabad City during the earthquake in Bhuj on 26(th) January 2001. An attempt has been made to understand the reasons for the failure of multistoreyed buildings founded on soft alluvial deposits in Ahmedabad. Standard Penetration test at a site very close to the Sabarmati river belt was carried out for geotechnical investigations. The program SHAKE91, widely used in the field of earthquake engineering for computing the seismic response of horizontally layered soil deposits, was used to analyse the soil profile at the selected site considering the ground as one dimensional layered elastic system. The ground accelerations recorded at the ground floor of the Regional Passport Staff Quarters building, which is very close to the investigated site, was used as input motion. Also, Finite Element Analysis was carried out for different configurations of multistorey building frames for evaluating their natural frequencies and is compared with the predominant frequency of the layered soil system. The results reveal that the varying degree of damage to multistorey buildings in the close proximity of Sabarmati river area was essentially due to the large amplification of the ground and the near resonance condition.

A k-epsilon model for turbulent weld pool convection in gas metal arc welding process

In this paper, we present a modified k - epsilon model capable of addressing turbulent weld-pool convection in a GMAW process, taking into account the morphology of the phase change interface during a Gas Metal Arc Welding (GMAW) process. A three-dimensional turbulence mathematical model has been developed to study the heat transfer and fluid flow within the weld pool by considering the combined effect of three driving forces, viz., buoyancy, Lorentz force and surface tension (Marangoni convection). Mass and energy transports by the droplets are considered through the thermal analysis of the electrode. The falling droplet's heat addition to the molten pool is considered to be a volumetric heat source distributed in an imaginary cylindrical cavity ("cavity model") within the weld pool. This nature of heat source distribution takes into account the momentum and the thermal, energy of the falling droplets. The numerically predicted weld pool dimensions both from turbulence and laminar models are then compared with the experimental post-weld results sectioned across the weld axis. The above comparison enables us to analyze the overall effects of turbulent convection on the nature of heat and fluid flow and hence on the weld pool shape/size during the arc welding processes.

Pulsed plasma treatment of polluted gas using wet/low temperature corona reactors

pplication of pulsed plasma for gas cleaning is gaining prominence in recent years mainly from the energy consideration point of view. Normally, gas treatment is carried out, at or above room temperature, by a conventional dry type corona reactor. However, this treatment is still inadequate in the removal of certain stable gases present in the exhaust/flue gas mixture. The authors report some interesting results of the treatment of such stable gases with pulsed plasma at very low ambient temperature. Also reported in the paper is an improvement in DeNO/DeNOx efficiency using unconventional wet-type reactors, designed and fabricated by the authors, operating at different ambient temperatures. Apart from laboratory tests on simulated gas mixtures, field tests were also carried out on the exhaust gas of a 8 kW diesel engine. Further, an attempt was made to test the feasibility of a helical wire as a corona electrode in place of the conventional straight wire electrode. A comparative analysis of the various tests is presented together with a note on the energy consideration

Pulsed plasma treatment of polluted gas using wet/low temperature corona reactors

Application of pulsed plasma for gas cleaning is gaining prominence in recent years mainly from the energy consideration point of view. Normally, gas treatment is carried out, at or above room temperature, by a conventional dry type corona reactor. However, this treatment is still inadequate in the removal of certain stable gases present in the exhaust/flue gas mixture. The authors report some interesting results of the treatment of such stable gases with pulsed plasma at very low ambient temperature. Also reported in the paper is an improvement in DeNO/DeNOx efficiency using unconventional wet-type reactors, designed and fabricated by the authors, operating at different ambient temperatures. Apart from laboratory tests on simulated gas mixtures, field tests were also carried out on the exhaust gas of a 8 kW diesel engine. Further, an attempt was made to test the feasibility of a helical wire as a corona electrode in place of the conventional straight wire electrode. A comparative analysis of the various tests is presented together with a note on the energy consideration

Design and performance analysis of a signal detector based on suprathreshold stochastic resonance

This paper presents the design and performance analysis of a detector based on suprathreshold stochastic resonance (SSR) for the detection of deterministic signals in heavy-tailed non-Gaussian noise. The detector consists of a matched filter preceded by an SSR system which acts as a preprocessor. The SSR system is composed of an array of 2-level quantizers with independent and identically distributed (i.i.d) noise added to the input of each quantizer. The standard deviation sigma of quantizer noise is chosen to maximize the detection probability for a given false alarm probability. In the case of a weak signal, the optimum sigma also minimizes the mean-square difference between the output of the quantizer array and the output of the nonlinear transformation of the locally optimum detector. The optimum sigma depends only on the probability density functions (pdfs) of input noise and quantizer noise for weak signals, and also on the signal amplitude and the false alarm probability for non-weak signals. Improvement in detector performance stems primarily from quantization and to a lesser extent from the optimization of quantizer noise. For most input noise pdfs, the performance of the SSR detector is very close to that of the optimum detector. (C) 2012 Elsevier B.V. All rights reserved.

Anomalous triple gauge boson couplings in e(-)e(+) -> gamma gamma for noncommutative standard model

We investigate e(+)e(-) -> gamma gamma process within the Seiberg-Witten expanded noncommutative standard model (NCSM) scenario in the presence of anomalous triple gauge boson couplings. This study is done with and without initial beam polarization and we restrict ourselves to leading order effects of noncommutativity i.e. O(Theta). The noncommutative (NC) corrections are sensitive to the electric component ((Theta) over bar (E)) of NC parameter. We include the effects of Earth's rotation in our analysis. This study is done by investigating the effects of noncommutativity on different time averaged cross section observables. We have also defined forward backward asymmetries which will be exclusively sensitive to anomalous couplings. We have looked into the sensitivity of these couplings at future experiments at the International Linear Collider (ILC). This analysis is done under realistic ILC conditions with the center of mass energy (cm.) root s = 800 GeV and integrated luminosity L = 500 fb(-1). The scale of noncommutativity is assumed to be Lambda = 1 TeV. The limits on anomalous couplings of the order 10(-1) from forward backward asymmetries while much stringent limits of the order 10(-2) from total cross section are obtained if no signal beyond SM is seen. (C) 2012 Elsevier B.V. All rights reserved.

Time and Frequency Domain Finite Element Models for Axial Wave Analysis in Hyperelastic Rods

The propagation of axial waves in hyperelastic rods is studied using both time and frequency domain finite element models. The nonlinearity is introduced using the Murnaghan strain energy function and the equations governing the dynamics of the rod are derived assuming linear kinematics. In the time domain, the standard Galerkin finite element method, spectral element method, and Taylor-Galerkin finite element method are considered. A frequency domain formulation based on the Fourier spectral method is also developed. It is found that the time domain spectral element method provides the most efficient numerical tool for the problem considered.

Isomeric identification of methylated naphthalenes using gas phase infrared spectroscopy

We report gas phase mid-infrared spectra of 1- and 2- methyl naphthalenes at 0.2 cm(-1) resolution. Assignment of observed bands have been made using scaled quantum mechanical (SQM) calculations where the force fields rather the frequencies are scaled to find a close fit between observed and calculated bands. The structure of the molecules has been optimized using B3LYP level of theory in conjunction with standard 6-311G** basis set to obtain the harmonic frequencies. Using the force constants in Cartesian coordinates from the Gaussian output, scaled force field calculations are carried out using a modified version of the UMAT program in the QCPE package. Potential energy distributions of the normal modes obtained from such calculations helped us assign the observed bands and identify the unique features of the spectra of 1- and 2-MNs which are important for their isomeric identification.

Scaling analysis: Equivalence of convective and radiative heating of levitated droplet

This letter develops theoretical relationships for equilibrium timescale and temperature scale of a vaporizing droplet in a convective and a radiative environment. The transient temperature normalized by the respective scales exhibits a unified profile for both modes of heating. The analysis allows for the prediction of the required laser flux to show its equivalence in a corresponding heated gas stream. The theoretical equivalence shows good agreement with experiments across a range of droplet sizes. Simple experiments can be conducted in a levitator to extrapolate information in realistic convective environments like combustion and spray drying. (C) 2012 American Institute of Physics. http://dx.doi.org/10.1063/1.4720092]